Cholesterol amperometric biosensor based on cytochrome P450scc

Electrochemical Probing of Human Liver Subcellular S9 Fractions for Drug Metabolite Synthesis

Human liver subcellular fractions, including liver microsomes (HLM), liver cytosol fractions, and S9 fractions, are extensively utilized in in vitro assays to predict liver metabolism. The S9 fractions are supernatants of human liver homogenates that contain both microsomes and cytosol, which include most cytochrome P450 (CYP) enzymes and soluble phase II enzymes such as glucuronosyltransferases and sulfotransferases. This study reports on the direct electrochemistry and biocatalytic features of redox-active enzymes in S9 fractions for the first time. We investigated the electrochemical properties of S9 films by immobilizing them onto a high-purity graphite (HPG) electrode and performing cyclic voltammetry under anaerobic (Ar-saturated) and aerobic (O2-saturated) conditions. The heterogeneous electron transfer rate between the S9 film and the HPG electrode was found to be 14 ± 3 s-1, with a formal potential of -0.451 V vs. Ag/AgCl reference electrode, which confirmed the electrochemical activation of the FAD/FMN cofactor containing CYP450-reductase (CPR) as the electron receiver from the electrode. The S9 films have also demonstrated catalytic oxygen reduction under aerobic conditions, identical to HLM films attached to similar electrodes. Additionally, we investigated CYP activity in the S9 biofilm for phase I metabolism using diclofenac hydroxylation as a probe reaction and identified metabolic products using liquid chromatography-mass spectrometry (LC-MS). Investigating the feasibility of utilizing liver S9 fractions in such electrochemical assays offers significant advantages for pharmacological and toxicological evaluations of new drugs in development while providing valuable insights for the development of efficient biosensor and bioreactor platforms.

Highly sensitive electrochemical detection of cholesterol based on Au-Pt NPs/PAMAM-ZIF-67 nanomaterials

A cholesterol biosensor was constructed by bimetallic (Au and Pt) and poly(amidoamine)-zeolite imidazole framework (PAMAM-ZIF-67). First, PAMAM-ZIF-67 nanomaterial was immobilized onto the electrode, and then Au and Pt were modified on the electrode by the electro-deposition method. Subsequently, cholesterol oxidase (ChOx) and cholesterol esterase (ChEt) were fixed on the electrode. The stepwise modification procedures were recorded by impedance spectroscopy and voltammetry. The current response presented a linear relation to the logarithm of cholesterol content when content ranged between 0.00015 and 10.24 mM, and the minimum detection concentration reached 3 nM. The electrode was also used for the cholesterol assay in serum, which hinted at its potentially valuable in clinical diagnostics. An electrochemical biosensor based on gold nanoparticles, platinum nanoparticles, and polyamide-zeolitic imidazolate frameworks was developed for detection of cholesterol. First, polyamide-zeolitic imidazolate frameworks nanomaterial was fixed onto the electrode modified of mercaptopropionic acid by Au-S bond. Then, gold nanoparticles and platinum nanoparticles were electrodeposited on the above electrode. Subsequently, cholesterol oxidase and cholesterol esterase were co-immobilized on the surface of the modified electrode to fabricate the cholesterol biosensor. The biosensor has also been used for the measurement of cholesterol in human serum, which implied potential applications in biotechnology and clinical diagnostics.

Electrochemical devices for cholesterol detection

Cholesterol can be considered as a biomarker of illnesses such as heart and coronary artery diseases or arteriosclerosis. Therefore, the fast determination of its concentration in blood is interesting as a means of achieving an early diagnosis of these unhealthy conditions. Electrochemical sensors and biosensors have become a potential tool for selective and sensitive detection of this biomolecule, combining the analytical advantages of electrochemical techniques with the selective recognition features of modified electrodes. This review covers the different approaches carried out in the development of electrochemical sensors for cholesterol, differentiating between enzymatic biosensors and non-enzymatic systems, highlighting lab-on-a-chip devices. A description of the different modification procedures of the working electrode has been included and the role of the different functional materials used has been discussed.

Sensitive electrochemical detection of cholesterol using a portable paper sensor based on the synergistic effect of cholesterol oxidase and nanoporous gold

As a crucial biomarker for some diseases, the determination of cholesterol in human serum is of great significance for the diagnosis and prevention of these diseases. Hence, a portable cholesterol detection method is necessary for clinical and domestic applications. Here, a portable paper sensor was designed for cholesterol detection by modifying screen-printed electrode (SPE) with nanoporous gold (NPG). To achieve the reliable cholesterol detection, a synergistic strategy was proposed based on the oxidation of cholesterol by cholesterol oxidase (ChOx) and the reduction of oxidation product (H₂O₂) by NPG. Compared to existing electrochemical sensors, the resulting paper sensor exhibited a wider linear response in a range from 50 μM to 6 mM as well as a higher sensitivity of 32.68 μA mM^-1 cm^-2 with a lower detection limit of 8.36 μM. Moreover, the portable paper sensor presented strong anti-interference capability and stability in the detection of cholesterol in human serum, and the data detected by the portable paper sensor were consistent with that obtained by an automatic biochemical analyzer. These unique performances confirmed that the proposed paper sensor was a sensitive, reliable, and portable cholesterol detection method, making it a good choice for cholesterol detection.

Hydrogel Based Sensors for Biomedical Applications: An Updated Review

Biosensors that detect and convert biological reactions to a measurable signal have gained much attention in recent years. Between 1950 and 2017, more than 150,000 papers have been published addressing the applications of biosensors in different industries, but to the best of our knowledge and through careful screening, critical reviews that describe hydrogel based biosensors for biomedical applications are rare. This review discusses the biomedical application of hydrogel based biosensors, based on a search performed through Web of Science Core, PubMed (NLM), and Science Direct online databases for the years 2000⁻2017. In this review, we consider bioreceptors to be immobilized on hydrogel based biosensors, their advantages and disadvantages, and immobilization techniques. We identify the hydrogels that are most favored for this type of biosensor, as well as the predominant transduction strategies. We explain biomedical applications of hydrogel based biosensors including cell metabolite and pathogen detection, tissue engineering, wound healing, and cancer monitoring, and strategies for small biomolecules such as glucose, lactate, urea, and cholesterol detection are identified.

Direct electrochemistry of cholesterol oxidase and biosensing of cholesterol based on PSS/polymeric ionic liquid–graphene nanocomposite

In this work, a new biosensor based on PSS/polymeric ionic liquids–graphene nanocomposite with excellent conductivity, favourable biocompatibility and good film-forming properties was constructed to detect cholesterol.

Carbon Inverse Opal Rods for Nonenzymatic Cholesterol Detection

Carbon inverse opal rods made from silica photonic crystal rods are used for nonenzymatic cholesterol sensing. The characteristic reflection peak originating from the physical periodic structure works as sensing signals for quantitatively estimating cholesterol concentrations. Carbon inverse opal rods work both in cholesterol standard solutions and human serum. They are suitable for practical use in clinical diagnose.

Enzyme immobilization by entrapment within a gel network

This chapter provides a detailed description of the three immobilization methods based on the biomolecules entrapment into polymer matrices. The poly (vinyl alcohol) bearing styrylpyridinium groups (PVA-SbQ), a soluble pre-polymer bearing photo-cross-linkable groups, has widely been used to entrap enzymes, and several bioassays based on this immobilization matrix have been reported. Similarly, immobilization of enzymes via sol-gel has been described in this chapter. Sol-gel process is based on the ability to form solid metal or semi-metal oxides via the aqueous process of hydrolytically labile precursors. Enzymes can also be entrapped in an agarose gel. Contrary to synthetic polymers such as polyacrylamide, this matrix is biocompatible, non-toxic, provides natural microenvironment to the enzyme and also gives sufficient accessibility to electrons to shuttle between the enzyme and the electrode. The entrapment strategies are easy-to-perform, and permit to deposit enzyme, mediators, and additives in the same sensing layer. Moreover, the activity of the enzyme is preserved during the immobilization process, as biological element is not modified. Biosensors based on physically entrapped enzymes are often characterized by increased operational and storage stability.

Prototypes of newly conceived inorganic and biological sensors for health and environmental applications

This paper describes the optimal implementation of three newly conceived sensors for both health and environmental applications, utilizing a wide range of detection methods and complex nanocomposites. The first one is inorganic and based on matrices of calcium oxide, the second is based on protein arrays and a third one is based on Langmuir-Blodgett laccase multi-layers. Special attention was paid to detecting substances significant to the environment (such as carbon dioxide) and medicine (drug administration, cancer diagnosis and prognosis) by means of amperometric, quartz crystal microbalance with frequency (QCM_F) and quartz crystal microbalance with dissipation monitoring (QCM_D) technologies. The resulting three implemented nanosensors are described here along with proofs of principle and their corresponding applications.

Catabolism and biotechnological applications of cholesterol degrading bacteria

Cholesterol is a steroid commonly found in nature with a great relevance in biology, medicine and chemistry, playing an essential role as a structural component of animal cell membranes. The ubiquity of cholesterol in the environment has made it a reference biomarker for environmental pollution analysis and a common carbon source for different microorganisms, some of them being important pathogens such as Mycobacterium tuberculosis. This work revises the accumulated biochemical and genetic knowledge on the bacterial pathways that degrade or transform this molecule, given that the characterization of cholesterol metabolism would contribute not only to understand its role in tuberculosis but also to develop new biotechnological processes that use this and other related molecules as starting or target materials.

Nano-bio-technology and sensing chips: new systems for detection in personalized therapies and cell biology

Further advances in molecular medicine and cell biology also require new electrochemical systems to detect disease biomarkers and therapeutic compounds. Microelectronic technology offers powerful circuits and systems to develop innovative and miniaturized biochips for sensing at the molecular level. However, microelectronic biochips proposed in the literature often do not show the right specificity, sensitivity, and reliability required by biomedical applications. Nanotechnology offers new materials and solutions to improve the surface properties of sensing probes. The aim of the present paper is to review the most recent progress in Nano-Bio-Technology in the area of the development of new electrochemical systems for molecular detection in personalized therapy and cell culture monitoring.

Electrochemical Sensors for Clinic Analysis

Demanded by modern medical diagnosis, advances in microfabrication technology have led to the development of fast, sensitive and selective electrochemical sensors for clinic analysis. This review addresses the principles behind electrochemical sensor design and fabrication, and introduces recent progress in the application of electrochemical sensors to analysis of clinical chemicals such as blood gases, electrolytes, metabolites, DNA and antibodies, including basic and applied research. Miniaturized commercial electrochemical biosensors will form the basis of inexpensive and easy to use devices for acquiring chemical information to bring sophisticated analytical capabilities to the non-specialist and general public alike in the future.

Protein electrodes with direct electrochemical communication

Electrochemistry using direct electron transfer between an electrode and a protein or an enzyme has developed into a means for studying biological redox reactions and for bioanalytics, biosynthesis and bioenergetics. This review summarizes recent work on direct protein electrochemistry with special emphasis on our results in bioelectrocatalysis using isolated enzymes and enzyme-protein couples.

Anodic porous alumina as mechanical stability enhancer for LDL-cholesterol sensitive electrodes

In this work, to improve the mechanical stability of electrodes based on P450scc for LDL-cholesterol detection and measure, anodic porous alumina (APA) was used. This inorganic matrix, which pores can be tuned in diameter modifying the synthesis parameters, was realized with cavities 275 nm wide and 160 microm deep (as demonstrated with AFM and SEM measurement), to allow the immobilization of P450scc macromolecules preserving their electronic sensitivity to its native substrate, cholesterol. Even if the sensitivity of the APA+P450scc system was slightly reduced with respect to the pure P450scc system, the readout was stable for a much longer period of time, and the measures remained reproducible inside a proper confidentiality band, as demonstrated with several cyclic voltammetry measures. To optimize the adhesion of P450scc to APA, a layer of poly-L-lysine, a poly-cathion, was successfully implemented as intermediate organic structure.

Development of cholesterol biosensor based on immobilized cholesterol esterase and cholesterol oxidase on oxygen electrode for the determination of total cholesterol in food samples

The development of a cholesterol biosensor by co-immobilization of cholesterol esterase (ChEt) and cholesterol oxidase (ChOX) on oxygen electrode is described. The electrode consists of gold cathode and Ag/AgCl anode. The enzymes were immobilized by cross-linking with glutaraldehyde and Bovine Serum Albumin (BSA). The immobilized enzymatic membrane was attached to the tip of the electrode by a push cap system. The optimum pH and temperature of the sensor was determined, these are 6 and 25 degrees C respectively. The developed sensor was calibrated from 1-75 mg/dl of cholesterol palmiate and found linear in the range of 2-50 mg/dL. The calibration curve was drawn with V(i) (ppm/min)(initial velocity) vs different concentrations of cholesterol palmiate (mg/dL). The application of the sensor to determine the total cholesterol in different real food samples such as egg, meat was investigated. The immobilized enzymatic layer can be reused over 30 times and the stability of the enzymatic layer was studied up to 9 weeks.

Biosensor development in Russia

The review summarizes the current Russian research in the field of biological sensors for detection of carbohydrates, alcohols, medicines, enzyme inhibitors, toxicants, heavy metal ions, as well as viruses and microbial cells. Some of the presented works describe the analytical parameters of biosensors; other publications provide a basis for their development. The review covers mainly publications that have appeared over the past 10 years. As a whole, the collected material gives an idea of the main tendencies of biosensor development in Russia. The review is not meant to be comprehensive but highlights the major trends in this field in the last decade.

Bioanalytical device based on cholesterol oxidase-bonded SAM-modified electrodes

A rapid, simple and reproducible two-step method for constructing cholesterol biosensors by covalently bonding cholesterol oxidase (ChOx) to a 3,3'-dithiodipropionic acid di(N-succinimidyl ester) (DTSP)-modified gold electrode is described. Exhaustive characterizations of both the immobilization process and the morphological properties of the resulting ChOx monolayer were performed via a quartz crystal microbalance (QCM) and atomic force microscopy (AFM) operated under liquid conditions, respectively. In addition, scanning electrochemical microscopy (SECM) measurements were performed in order to check that the immobilized enzyme retains its catalytic activity. The replacement of the natural electron acceptor (O(2)) in the enzymatic reaction with an artificial mediator, hydroxymethylferrocene (HMF), was also studied. Finally, cholesterol was amperometrically determined by measuring the hydrogen peroxide produced during the enzymatic reaction at +0.5 V. The optimized cholesterol biosensor exhibited a sensitivity of 54 nA mM(-1) and a detection limit of 22 microM.

Immobilization of cholesterol esterase and cholesterol oxidase onto sol–gel films for application to cholesterol biosensor

Cholesterol oxidase (ChOx) and cholesterol esterase (ChEt) have been covalently immobilized onto tetraethylorthosilicate (TEOS) sol-gel films. The tetraethylorthosilicate sol-gel/ChEt/ChOx enzyme films thus prepared have been characterized using scanning electron microscopic (SEM), UV-vis spectroscopic, Fourier-transform-infrared (FTIR) spectroscopic and amperometric techniques, respectively. The results of photometric measurements carried out on tetraethylorthosilicate sol-gel/ChEt/ChOx reveal thermal stability up to 55 degrees C, response time as 180 s, linearity up to 780 mg dL(-1) (12 mM), shelf life of 1 month, detection limit of 12 mg dL(-1) and sensitivity as 5.4 x 10(-5) Abs. mg(-1) dL(-1).

A new format of electrodes for the electrochemical reduction of cytochromes P450

New approach to the electrochemical reduction of cytochromes P450 (P450s, CYPs) at electrodes chemically modified with appropriate substrates for P450s ("reverse" electrodes) was proposed. The method is based on the analysis of cyclic voltammograms, square-wave voltammograms and amperograms with subsequent determination of electrochemical characteristics such as catalytic current and redox potential. The sensitivity of proposed method is 0.2-1 nmol P450/electrode. The changes of maximal current and of redox potentials in square-wave voltammograms as well as the changes of catalytic current in amperometric experiments proved to be informative and reliable. Planar regime of screen-printed electrodes (strip-type sensors) enabled to utilise 20-60 microl of electrolyte volume. The enzyme-substrate pairs P450 2B4/benzphetamine and P450scc/cholesterol were investigated. Electrochemical parameters of electrodes with unspecific P450 substrates differed considerably from electrodes with appropriate substrates.